[bugfix] segv on pic_receive
[bugfix] segv on pic_receive

dcurrie/picrin,koba-e964/picrin,omasanori/picrin,koba-e964/picrin,leavesbnw/picrin,koba-e964/picrin,leavesbnw/picrin,leavesbnw/picrin,ktakashi/picrin,omasanori/picrin,ktakashi/picrin,ktakashi/picrin,picrin-scheme/picrin,dcurrie/picrin,picrin-scheme/picrin